Electrolyte for electrochemical device

ABSTRACT

The invention relates to an electrolyte for an electrochemical device. This electrolyte includes a first compound that is an ionic metal complex represented by the general formula (1); and at least one compound selected from special second to fourth compounds, fifth to ninth compounds respectively represented by the general formulas A a+ (PF 6   − ) a , A a+ (ClO 4   − ) a , A a+ (BF 4   − ) a , A a+ (AsF 6   − ) a , and A a+ (SbF 6   − ) a , and special tenth to twelfth compounds,  
                 
 
     The electrolyte is superior in cycle characteristics and shelf life as compared with conventional electrolytes.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an electrolyte, an ion conductorincluding the electrolyte, and electrochemical devices including theelectrolyte, such as lithium cells, lithium ion cells, electricaldouble-layer capacitors.

[0002] Accompanying the evolution of portable equipment in recent years,there has been active development of electrochemical devices utilizingelectrochemical phenomena, such as cells for use as their power suppliesand capacitors. In addition, electrochromic devices (ECD), in which acolor change occurs due to an electrochemical reaction, are examples ofelectrochemical devices for uses other than power supplies.

[0003] These electrochemical devices are typically composed of a pair ofelectrodes and an ion conductor filled between them. The ion conductorcontains a salt (AB) as an electrolyte, which is dissolved in a solvent,polymer or mixture thereof such that the salt is dissociated intocations (A⁺) and anions (B⁻), resulting in ionic conduction. In order toobtain the required level of ion conductivity for the device, it isnecessary to dissolve a sufficient amount of this electrolyte in solventor polymer. In actuality, there are many cases in which a solvent otherthan water is used, such as organic solvents and polymers. Electrolyteshaving sufficient solubility in such organic solvents and polymers arepresently limited to only a few types. For example, electrolytes havingsufficient solubility for use in lithium cells are only LiClO₄, LiPF₆,LiBF₄, LiAsF₆, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉) andLiCF₃SO₃. Although the cation type of the electrolyte is frequentlylimited by the device as is the case with the lithium ion of lithiumcells, any anion can be used for the electrolyte provided it satisfiesthe condition of having high solubility.

[0004] Amidst the considerable diversity of the application range ofthese devices, efforts are made to seek out the optimum electrolyte foreach application. Under the present circumstances, however, optimizationefforts have reached their limit due to the limited types of availableanions. In addition, existing electrolytes have various problems,thereby creating the need for an electrolyte having a novel anionportion. More specifically, since ClO₄ ion of LiClO₄ is explosive andAsF₆ ion of LiAsF₆ is toxic, they cannot be used for reasons of safety.Even the only practical electrolyte of LiPF₆ has problems including heatresistance and hydrolysis resistance. Although electrolytes ofLiN(CF₃SO₂)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉) and LiCF₃SO₃ arestable and high in ionic conductivity, they corrode the aluminumcollector inside the cell when a potential is applied. Therefore, theiruse presents difficulties.

SUMMARY OF THE INVENTION

[0005] It is therefore an object of the present invention to provide auseful novel electrolyte, a novel ion conductor containing theelectrolyte, and a novel electrochemical device containing the ionconductor.

[0006] According to the present invention, there is provided anelectrolyte for an electrochemical device. This electrolyte comprises:

[0007] a first compound that is an ionic metal complex represented bythe general formula (1); and

[0008] at least one compound selected from the group consisting ofsecond to fourth compounds respectively represented by the generalformulas (2) to (4), fifth to ninth compounds respectively representedby the general formulas A^(a+)(PF₆ ⁻)_(a), A^(a+)(ClO₄ ⁻)_(a),A^(a+)(BF₄ ⁻)_(a), A^(a+)(AsF₆ ⁻)_(a), and A^(a+)(SbF₆ ⁻)_(a), and tenthto twelfth compounds respectively represented by the general formulas(5) to (7),

[0009] wherein M is a transition metal selected from the groupconsisting of elements of groups 3-11 of the periodic table, or anelement selected from the group consisting of elements of groups 12-15of the periodic table;

[0010] A^(a+) represents a metal ion, hydrogen ion or onium ion;

[0011] a represents a number from 1 to 3; b represents a number from 1to 3; p is b/a; m represents a number from 1 to 4; q is 0 or 1;

[0012] R¹ represents a C₁-C₁₀ alkylene group, C₁-C₁₀ halogenatedalkylene group, C₄-C₂₀ arylene group or C₄-C₂₀ halogenated arylenegroup, these alkylene and arylene groups of said R¹ optionally havingsubstituents and hetero atoms, one of said R¹ being optionally bondedwith another of said R¹;

[0013] each of X¹ and X² independently represents O, S or NR²;

[0014] R² represents a hydrogen, C₁-C₁₀ alkyl group, C₁-C₁₀ halogenatedalkyl group, C₄-C₂₀ aryl group or C₄-C₂₀ halogenated aryl group, thesealkyl and aryl groups of said R² optionally having substituents andhetero atoms, at least two of said R² being optionally bonded togetherto form a ring;

[0015] each of x, y and z independently represents a number from 1 to 8

[0016] each of Y¹, Y² and Y³ independently represents a SO₂ group or COgroup; and

[0017] each of R³, R⁴ and R⁵ independently represents anelectron-attractive organic substituent optionally having a substituentor a hetero atom, at least two of said R³,R⁴ and R⁵ being optionallybonded together to form a ring, at least one of said R³, R⁴ and R⁵ beingoptionally bonded with an adjacent molecule to form a polymer.

[0018] According to the present invention, there is provided an ionconductor for an electrochemical device. This ion conductor comprisesthe electrolyte; and a member selected from the group consisting of anonaqueous solvent, a polymer and a mixture thereof, said memberdissolving therein said electrolyte.

[0019] According to the present invention, there is provided anelectrochemical device comprising (a) first and second electrodes; and(b) the ion conductor receiving therein said first and secondelectrodes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An electrolyte according to the present invention is superior incycle characteristics and shelf life as compared with conventionalelectrolytes. Thus, the electrolyte can advantageously be used forelectrochemical devices such as lithium cell, lithium ion cell andelectrical double-layer capacitor.

[0021] According to the invention, the alkyl groups, halogenated alkylgroups, aryl groups and halogenated aryl groups, which are contained inthe ionic metal complex and the raw materials for synthesizing the same,may be branched and/or may have other functional groups such as hydroxylgroups and ether bonds.

[0022] The followings are specific four examples of the ionic metalcomplex represented by the general formula (1) of the present invention.

[0023] Here, although lithium ion is indicated as an example of A^(a+)of the general formula (1), examples of other cations that can be usedother than lithium ion include sodium ion, potassium ion, magnesium ion,calcium ion, barium ion, cesium ion, silver ion, zinc ion, copper ion,cobalt ion, iron ion, nickel ion, manganese ion, titanium ion, lead ion,chromium ion, vanadium ion, ruthenium ion, yttrium ion, lanthanoid ion,actinoid ion, tetrabutylammonium ion, tetraethylammonium ion,tetramethylammonium ion, triethylmethylammonium ion, triethylammoniumion, pyridinium ion, imidazolium ion, hydrogen ion,tetraethylphosphonium ion, tetramethylphosphonium ion,tetraphenylphosphonium ion, triphenylsulfonium ion, andtriethylsulfonium ion. In the case of considering the application of theionic metal complex for electrochemical devices and the like, lithiumion, tetraalkylammonium ion and hydrogen ion are preferable. As shown inthe general formula (1), the valency (valence) of the A^(a+) cation ispreferably from 1 to 3. If the valency is larger than 3,the problemoccurs in which it becomes difficult to dissolve the ionic metal complexin solvent due to the increase in crystal lattice energy. Consequently,in the case of requiring solubility of the ionic metal complex, avalency of 1 is preferable. As shown in the general formula (1), thevalency (b⁻) of the anion is similarly preferably from 1 to 3,and avalency of 1 is particularly preferable. The constant p expresses theratio of the valency of the anion to the valency of the cation, namelyb/a.

[0024] In the general formula (1), M at the center of the ionic metalcomplex of the present invention is selected from elements of groups3-15 of the periodic table. It is preferably Al, B, V, Ti, Si, Zr, Ge,Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb, and more preferablyAl, B or P. Although it is possible to use various elements for the Mother than these preferable examples, synthesis is relatively easy inthe case of using Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta,Bi, P, As, Sc, Hf or Sb. In addition to ease of synthesis, the ionicmetal complex has excellent properties in terms of low toxicity,stability and production cost in the case of using Al, B or P.

[0025] In the general formula (1), the organic or inorganic portionbonded to M is referred to as the ligand. As mentioned above, R¹ in thegeneral formula (1) represents a C₁-C₁₀ alkylene group, C₁-C₁₀halogenated alkylene group, C₄-C₂₀ arylene group or C₄-C₂₀ halogenatedarylene group. These alkylene and arylene groups optionally havesubstituents and hetero atoms. For example, hydrogen of these alkyleneand arylene groups may be replaced with halogen, an acyclic or cyclicalkyl group, aryl group, alkenyl group, alkoxy group, aryloxy group,sulfonyl group, amino group, cyano group, carbonyl group, acyl group,amide group or hydroxyl group. Furthermore, carbon of the alkylene andarylene groups may be replaced with nitrogen, sulfur or oxygen. When thefirst compound has a plurality of R¹ in the molecule, these R¹ may bebonded together. In this case, the ligand may be in the form like thatof ethylenediaminetetraacetic acid.

[0026] Each of X¹ and X² in the general formula (1) independentlyrepresents O, S or NR², and is bonded to M through its hetero atom (O, Sor N). Although the bonding of an atom other than O, S or N is notimpossible, the synthesis becomes extremely bothersome. The ionic metalcomplex represented by the general formula (1) is characterized by theseligands forming a chelate structure with M since there is bonding with Mby X¹ and X² within the same ligand. As a result of this chlelation, theheat resistance, chemical stability and hydrolysis resistance of theionic metal complex are improved. Although constant q in this ligand iseither 0 or 1,in the case of 0 in particular, since the chelate ringbecomes a five-member ring, chelating effects are demonstrated mostprominently, making this preferable due to the resulting increase instability.

[0027] In the general formula (1), R² represents a hydrogen, C₁-C₁₀alkyl group, C₁-C₁₀ halogenated alkyl group, C₄-C₂₀ aryl group or C₄-C₂₀halogenated aryl group. These alkyl and aryl groups optionally havesubstituents and hetero atoms, and at least two of R² are optionallybonded together to form a ring.

[0028] In the general formula (1), the value of the constant m relatingto the number of the above-mentioned ligands depends on the type of thecentral M. In fact, m is preferably from 1 to 4.

[0029] According to a first preferred embodiment of the invention, theelectrolyte contains the ionic metal complex represented by the generalformula (1) and another component that is at least one compound selectedfrom the above-mentioned second to fourth compounds represented by thegeneral formulas (2), (3) and (4). Examples of these compounds areLiCF₃SO₃, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉) andLiC(SO₂CF₃)₃. If the ionic metal complex is omitted in the firstpreferred embodiment, the following problem occurs. That is, the anothercomponent corrodes the aluminum collector inside the cell when apotential is applied. With this, the capacity is lowered by repeatingthe charge and discharge cycle. In contrast, according to the firstpreferred embodiment, the aluminum collector corrosion can unexpectedlybe prevented by using a mixture of the ionic metal complex and theanother component. The reason of this is not clear. It is, however,assumed that the ionic metal complex is slightly decomposed on theelectrode surface and that a film of the ionic metal complex's ligand isformed on the aluminum surface, thereby preventing the aluminumcollector corrosion.

[0030] According to a second preferred embodiment of the invention, theelectrolyte contains the ionic metal complex represented by the generalformula (1) and another component that is at least one compound selectedfrom the above-mentioned fifth to ninth compounds respectivelyrepresented by the general formulas A^(a+)(PF₆ ⁻)_(a), A^(a+)(ClO₄⁻)_(a), A^(a+)(BF₄ ⁻)_(a), A^(a+)(AsF₆ ⁻)_(a), and A^(a+)(SbF₆ ⁻)_(a)where A^(a+) is preferably the same ion as that in the general formula(1). If the ionic metal complex is omitted in the second preferredembodiment, the following problem occurs. That is, the anion(s) tends tobe pyrolyzed at a high temperature of 60° C. or higher, therebygenerating a Lewis acid(s). This Lewis acid decomposes the solvent andmakes the electrochemical device inferior in performance and lifetime.Furthermore, the omission of the ionic metal complex causes hydrolysisof the anion(s) when the electrolyte is contaminated with a very smallamount of water. This hydrolysis generates an acid(s) that makes theelectrochemical device inferior in performance and lifetime. Incontrast, according to the second preferred embodiment, theabove-mentioned pyrolysis and hydrolysis can unexpectedly be preventedby using a mixture of the ionic metal complex and the another component.The reason of this is not clear. It is, however, assumed that theproperties of the solution as a whole change somehow to achieve thisprevention by a certain interaction between the ionic metal complex andthe another component.

[0031] According to a third preferred embodiment of the invention, theelectrolyte contains the ionic metal complex represented by the generalformula (1) and another component that is at least one compound selectedfrom the above-mentioned tenth to twelfth compounds represented by thegeneral formulas (5), (6) and (7). Examples of these compounds areCF₃CH₂OSO₃Li, (CF₃)₂CHOSO₃Li, (CF₃CH₂OSO₂)₂NLi, ((CF₃)₂CHOSO₂)₂NLi,(CF₃CH₂OSO₂)((CF₃)₂CHOSO₂)NLi, ((CF₃)₃COSO₂)₂NLi, and((CF₃)₂CHOSO₂)₃CLi. Further examples are polymers and oligomers such as[N(Li)SO₂OCH₂(CF₂)₄CH₂OSO₂]_(n) where n is a number of 2-1,000. If theionic metal complex is omitted in the third preferred embodiment, thefollowing problem occurs. That is, the another component corrodes thealuminum collector inside the cell when a potential is applied. Withthis, the capacity is lowered by repeating the charge and dischargecycle. In contrast, according to the third preferred embodiment, thealuminum collector corrosion can unexpectedly be prevented by using amixture of the ionic metal complex and the another component. The reasonof this is not clear. It is, however, assumed that the ionic metalcomplex is slightly decomposed on the electrode surface and that a filmof the ionic metal complex's ligand is formed on the aluminum surface,thereby preventing the aluminum collector corrosion.

[0032] In the invention, the molar ratio of the ionic metal complex tothe at least one compound is preferably 1:99 to 99:1 (or a range from5:95 to 95:5), more preferably 20:80 to 80:20 (or a range from 30:70 to70:30), in view of improving the electrochemical device in cyclecharacteristics and shelf life. If this ratio is less than 1:99 (or5:95), it may become insufficient to prevent the above-mentionedaluminum corrosion and/or the above-mentioned pyrolysis and hydrolysis,thereby making the electrolyte inferior in cycle characteristics andshelf life. If the ratio is greater than 99:1 (or 95:5), advantages ofadding the at least one compound to increase ionic conductivity andelectrochemical stability may become insufficient.

[0033] In the case of preparing an electrochemical device of the presentinvention, its basic structural elements are ion conductor, negativeelectrode, positive electrode, collector, separator, container and thelike.

[0034] A mixture of electrolyte and non-aqueous solvent or polymer isused as the ion conductor. If a non-aqueous solvent is used, theresulting ion conductor is typically referred to as an electrolyticsolution, while if a polymer is used, it is typically referred to as apolymer solid electrolyte. Non-aqueous solvent may also be contained asplasticizer in polymer solid electrolytes.

[0035] There are no particular restrictions on the non-aqueous solventprovided it is an aprotic solvent that is able to dissolve anelectrolyte of the present invention, and examples of this non-aqueoussolvent that can be used include carbonates, esters, ethers, lactones,nitrites, amides and sulfones. In addition, the solvent can either beused alone or in the form of a mixture of two or more types of solvent.Specific examples of the solvent include propylene carbonate, ethylenecarbonate, diethyl carbonate, dimethyl carbonate, methylethyl carbonate,dimethoxyethane, acetonitrile, propionitrile, tetrahydrofuran,2-methyltetrahydrofuran, dioxane, nitromethane, N,N-dimethylformamide,dimethylsulfoxide, sulfolane and γ-butyrolactone.

[0036] In case that A^(a+) of the general formula (1) is lithium ion,the non-aqueous solvent of an electrolytic solution is preferably amixture of a first aprotic solvent having a dielectric constant of 20 orgreater and a second aprotic solvent having a dielectric constant of 10or less. In fact, lithium salt has a low solubility in the secondaprotic solvent (e.g., diethyl ether and dimethyl carbonate). Therefore,it may be difficult to obtain a sufficient ionic conductivity by usingonly the second aprotic solvent. In contrast, lithium salt has a highsolubility in the first aprotic solvent. The resulting solution is,however, high in viscosity. Thus, it may be difficult to obtain asufficient ionic conductivity by using only the first aprotic solvent,too. In contrast, it becomes possible to gain a suitable solubility anda suitable ionic mobility by using a mixture of the first and secondaprotic solvents, thereby making it possible to obtain a sufficientionic conductivity.

[0037] There are no particular restrictions on the polymer to be mixedwith the electrolytes of the invention provided it is an aproticpolymer. Examples of such polymer include polymers having polyethyleneoxide on their main chain or side chain, homopolymers or copolymers ofpolyvinylidene fluoride, methacrylate polymers and polyacrylonitrile. Inthe case of adding plasticizer to these polymers, the above-mentionedaprotic non-aqueous solvent can be used. The total concentration of theelectrolytes of the present invention in these ion conductors ispreferably 0.1 mol/dm³ or more up to the saturated concentration, andmore preferably from 0.5 mol/dm³ to 1.5 mol/dm³. If the concentration islower than 0.1 mol/dm³, ion conductivity may become too low.

[0038] There are no particular restrictions on the negative electrodematerial for preparing an electrochemical device. In the case of lithiumcell, lithium metal (metallic lithium) or an alloy of lithium andanother metal can be used. In the case of a lithium ion cell, it ispossible to use an intercalation compound containing lithium atoms in amatrix of another material, such as carbon, natural graphite or metaloxide. This carbon can be obtained by baking polymer, organic substance,pitch or the like. In the case of electrical double-layer capacitor, itis possible to use activated carbon, porous metal oxide, porous metal,conductive polymer and so forth.

[0039] There are no particular restrictions on the positive electrodematerial. In the case of lithium cell or lithium ion cell,lithium-containing oxides such as LiCoO₂,LiNiO₂, LiMnO₂ and LiMn2O₄;oxides such as TiO₂, V₂O₅ and MoO_(3;) sulfides such as TiS₂ and FeS;and electrically conductive polymers such as polyacetylene,polyparaphenylene, polyaniline or polypyrrole can be used. In the caseof electrical double-layer capacitor, activated carbon, porous metaloxide, porous metal, electrically conductive polymer and so forth can beused.

[0040] The following nonlimitative examples are illustrative of thepresent invention. In fact, Examples 1-1 to 1-5 are illustrative of theabove-mentioned first preferred embodiment of the invention, andExamples 2-1 to 2-4 are illustrative of the above-mentioned secondpreferred embodiment of the invention, and Examples 3-1 to 3-4 areillustrative of the above-mentioned third preferred embodiment of theinvention.

EXAMPLE 1-1

[0041] A lithium borate derivative, represented by the followingformula, and LiN(SO₂C₂F₅)₂ were dissolved in a mixture of ethylenecarbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 by volume) toprepare an electrolytic solution having a lithium borate derivativeconcentration of 0;05 mol/liter and a LiN(SO₂C₂F₅)₂ concentration of0.95 mol/liter.

[0042] Then, ion conductivity of the electrolytic solution was measuredwith an alternating current bipolar-type cell. As a result, the ionconductivity was 7.3 mS/cm at 25° C.

[0043] A corrosion test of an aluminum collector was performed using theabove-mentioned electrolytic solution. A beaker type cell was used forthe test cell, using aluminum for the working electrode, and lithiummetal (metallic lithium) for the counter electrode and referenceelectrode. When the working electrode was held at 5 V (Li/Li⁺), therewas no flow of current whatsoever. Following testing, although thesurface of the working electrode was observed by SEM, there were nochanges observed in comparison with that before testing.

[0044] A charging and discharging test of an actual cell was conductedusing the above-mentioned electrolytic solution. The test cell (halfcell) was prepared in the manner described below. The positive electrodewas prepared by mixing 5 parts by weight of polyvinylidene fluoride(PVDF) as a binder and 5 parts by weight of acetylene black as aconductor with 90 parts by weight of a LiCoO₂ powder followed by theaddition of N,N-dimethylformamide to form a paste. This paste wasapplied to an aluminum foil and allowed to dry to obtain the testpositive electrode. Lithium metal was used for the negative electrode. Aglass fiber filter as a separator was impregnated with the electrolyticsolution, thereby assembling the cell.

[0045] Next, a constant current charging and discharging test wasconducted as described below. The current density was 0.35 mA/cm² forboth charging and discharging, while charging was performed until 4.2 Vand discharging until 3.0 V (vs. Li/Li⁺). As a result, the initialdischarge capacity was 118 mAh/g (the positive electrode capacity).Although charging and discharging were repeated 100 times, results wereobtained in which the capacity of the 100^(th) cycle was 93% of theinitial capacity.

EXAMPLE 1-2

[0046] A lithium borate derivative, represented by the same formula asthat of Example 1-1,and LiN(SO₂CF₃)₂ were dissolved in a mixture ofpropylene carbonate (PC) and diethyl carbonate (DEC) (PC:DEC=1:1 byvolume) to prepare an electrolytic solution having a lithium boratederivative concentration of 0.10 mol/liter and a LiN(SO₂CF₃)₂concentration of 0.90 mol/liter. Then, ion conductivity of theelectrolytic solution was measured with an alternating currentbipolar-type cell. As a result, the ion conductivity was 8.9 mS/cm at25° C.

[0047] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0048] The test cell (half cell) was prepared in the same manner as thatof Example 1-1,and a constant current charging and discharging test wasconducted in the same manner as that of Example 1-1. As a result, theinitial discharge capacity was 115 mAh/g (the positive electrodecapacity). Although charging and discharging were repeated 100 times,results were obtained in which the capacity of the 100^(th) cycle was85% of the initial capacity.

EXAMPLE 1-3

[0049] A lithium borate derivative, represented by the same formula asthat of Example 1-1,and LiN(SO₂CF₃)(SO₂C₄F₉) were dissolved in a mixtureof ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 byvolume) to prepare an electrolytic solution having a lithium boratederivative concentration of 0.05 mol/liter and a LiN(SO₂CF₃)(SO₂C₄F₉)concentration of 0.95 mol/liter. Then, ion conductivity of theelectrolytic solution was measured with an alternating currentbipolar-type cell. As a result, the ion conductivity was 6.5 mS/cm at25° C.

[0050] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0051] The test cell (half cell) was prepared in the same manner as thatof Example 1-1,and a constant current charging and discharging test wasconducted in the same manner as that of Example 1-1. As a result, theinitial discharge capacity was 120 mAh/g (the positive electrodecapacity). Although charging and discharging were repeated 100 times,results were obtained in which the capacity of the 100^(th) cycle was91% of the initial capacity.

EXAMPLE 1-4

[0052] A lithium borate derivative, represented by the same formula asthat of Example 1-1,and LiN(SO₂CF₃)(SO₂C₄F₉) were dissolved in a mixtureof ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 byvolume) to prepare an electrolytic solution having a lithium boratederivative concentration of 0.95 mol/liter and a LiN(SO₂CF₃)(SO₂C₄F₉)concentration of 0.05 mol/liter. Then, ion conductivity of theelectrolytic solution was measured with an alternating currentbipolar-type cell. As a result, the ion conductivity was 6.9 mS/cm at25° C.

[0053] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0054] The test cell (half cell) was prepared in the same manner as thatof Example 1-1,and a constant current charging and discharging test wasconducted in the same manner as that of Example 1-1. As a result, theinitial discharge capacity was 120 mAh/g (the positive electrodecapacity). Although charging and discharging were repeated 100 times,results were obtained in which the capacity of the 100^(th) cycle was94% of the initial capacity.

EXAMPLE 1-5

[0055] A solution was prepared by adding acetonitrile to 70 parts byweight of a polyethylene oxide (average molecular weight: 10,000). Then,5 parts by weight of a lithium borate derivative, represented by thesame formula as that of Example 1-1,and 25 parts by weight ofLiN(SO₂CF₃)(SO₂C₄F₉) were added to the solution. The resulting mixturewas cast on a glass, followed by drying to remove the acetonitrile. Withthis, a polymer solid electrolyte film was prepared.

[0056] A corrosion test of an aluminum collector was performed using alaminate including the solid electrolyte film interposed between analuminum electrode (working electrode) and a lithium electrode. Thislaminate was prepared by press welding. When the working electrode washeld at 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0057] The test cell (half cell) was prepared in the same manner as thatof Example 1-1,except in that the polymer solid electrolyte film wasused in place of the electrolytic solution and the separator. Then, aconstant current charging and discharging test was conducted at 70° C.as described below. The current density was 0.1 mA/cm² for both chargingand discharging, while charging was performed until 4.2 V anddischarging until 3.0 V (vs. Li/Li⁺). As a result, the initial dischargecapacity was 120 mAh/g (the positive electrode capacity). Althoughcharging and discharging were repeated 100 times, results were obtainedin which the capacity of the 100^(th) cycle was 89% of the initialcapacity.

Comparative Example 1-1

[0058] At first, LiN(SO₂C₂F₅)₂ was dissolved in a mixture of ethylenecarbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 by volume) toprepare an electrolytic solution having a LiN(SO₂C₂F₅)₂ concentration of1.0 mol/liter.

[0059] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), corrosion current was observed. Following testing, thesurface of the working electrode was observed by SEM. With this, manypits were observed on its surface. It is assumed that these pits werecaused by corrosion.

[0060] The test cell (half cell) was prepared in the same manner as thatof Example 1-1,and a constant current charging and discharging test wasconducted in the same manner as that of Example 1-1. As a result, theinitial discharge capacity was 117 mAh/g (the positive electrodecapacity). Although charging and discharging were repeated 100 times,results were obtained in which the capacity of the 100^(th) cycle was69% of the initial capacity.

Comparative Example 1-2

[0061] At first, LiN(SO₂CF₃)₂ was dissolved in a mixture of propylenecarbonate (PC) and diethyl carbonate (DEC) (PC:DEC=1:1 by volume) toprepare an electrolytic solution having a LiN(SO₂CF³)₂ concentration of1.0 mol/liter.

[0062] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), corrosion current was observed. Following testing, thesurface of the working electrode was observed by SEM. With this, manypits were observed on its surface. It is assumed that these pits werecaused by corrosion.

[0063] The test cell (half cell) was prepared in the same manner as thatof Example 1-1,and a constant current charging and discharging test wasconducted in the same manner as that of Example 1-1. As a result, theinitial discharge capacity was 112 mAh/g (the positive electrodecapacity). Although charging and discharging were repeated 100 times,results were obtained in which the capacity of the 100^(th) cycle was67% of the initial capacity.

Comparative Example 1-3

[0064] At first, LiN(SO₂CF₃)(SO₂C₄F₉) was dissolved in a mixture ofethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 byvolume) to prepare an electrolytic solution having aLiN(SO₂CF₃)(SO₂C₄F₉) concentration of 1.0 mol/liter.

[0065] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), corrosion current was observed. Following testing, thesurface of the working electrode was observed by SEM. With this, manypits were observed on its surface. It is assumed that these pits werecaused by corrosion.

[0066] The test cell (half cell) was prepared in the same manner as thatof Example 1-1,and a constant current charging and discharging test wasconducted in the same manner as that of Example 1-1. As a result, theinitial discharge capacity was 118 mAh/g (the positive electrodecapacity). Although charging and discharging were repeated 100 times,results were obtained in which the capacity of the 100^(th) cycle was74% of the initial capacity.

EXAMPLE 2-1

[0067] An electrolytic solution was prepared by the same manner as thatof Example 1-1,except that LiN(SO₂C₂F₅)₂ was replaced with LiPF₆. Thiselectrolytic solution had a lithium borate derivative concentration of0.05 mol/liter and a LiPF₆ concentration of 0.95 mol/liter.

[0068] A charging and discharging test of an actual cell was conductedusing the above-mentioned electrolytic solution. The test cell wasprepared in the manner described below. The positive electrode of LiCoO₂was prepared by the same manner as that of Example 1-1. The negativeelectrode of natural graphite was prepared by mixing 10 parts by weightof polyvinylidene fluoride (PVDF) as a binder with 90 parts by weight ofa natural graphite powder followed by the addition ofN,N-dimethylformamide to form a slurry. This slurry was applied to ancopper foil and allowed to dry at 150° C. for 12 hr to obtain the testnegative electrode. A polyethylene separator was impregnated with theelectrolytic solution, thereby assembling the cell.

[0069] Next, a constant current charging and discharging test wasconducted at 70° C. under the following conditions. The current densitywas 0.35 mA/cm² for both charging and discharging, while charging wasperformed until 4.2 V and discharging until 3.0 V (vs. Li/Li⁺). Althoughcharging and discharging were repeated 500 times, results were obtainedin which the capacity of the 500^(th) cycle was 83% of the initialcapacity.

EXAMPLE 2-2

[0070] An electrolytic solution was prepared by substantially the samemanner as that of Example 1-2,in which LiN(SO₂CF₃)₂ was replaced withLiPF₆. The resulting electrolytic solution had a lithium boratederivative concentration of 0.10 mol/liter and a LiPF₆ concentration of0.90 mol/liter.

[0071] The test cell was prepared in the same manner as that of Example2-1,and a constant current charging and discharging test was conductedin the same manner as that of Example 2-1. The capacity of the 500^(th)cycle was 84% of the initial capacity.

EXAMPLE 2-3

[0072] An electrolytic solution was prepared by substantially the samemanner as that of Example 1-3,in which LiN(SO₂CF₃)(SO₂C₄F₉) was replacedwith LiBF₄. The resulting electrolytic solution had a lithium boratederivative concentration of 0.05 mol/liter and a LiBF₄ concentration of0.95 mol/liter.

[0073] The test cell was prepared in the same manner as that of Example2-1,and a constant current charging and discharging test was conductedin the same manner as that of Example 2-1. The capacity of the 500^(th)cycle was 79% of the initial capacity.

EXAMPLE 2-4

[0074] A solution was prepared by adding acetonitrile to 80 parts byweight of a polyethylene oxide (average molecular weight: 10,000). Then,10 parts by weight of a lithium borate derivative, represented by thesame formula as that of Example 1-1,and 10 parts by weight of LiPF₆ wereadded to the solution. The resulting mixture was cast on a glass,followed by drying to remove the acetonitrile. With this, a polymersolid electrolyte film was prepared.

[0075] The test cell was prepared in the same manner as that of Example2-1 except in that the polymer solid electrolyte film was used in placeof the electrolytic solution and the separator. In fact, LiCoO₂ was usedas a positive electrode material, and natural graphite was used as anegative electrode material. A constant current charging and dischargingtest was conducted at 70° C. under the following conditions. The currentdensity was 0.1 mA/cm² for both charging and discharging, while chargingwas performed until 4.2 V and discharging until 3.0 V (vs. Li/Li⁺). As aresult, the initial discharge capacity was 120 mAh/g (the positiveelectrode capacity). Although charging and discharging were repeated 500times, results were obtained in which the capacity of the 500^(th) cyclewas 85% of the initial capacity.

Comparative Example 2-1

[0076] At first, LiPF₆ was dissolved in a mixture of ethylene carbonate(EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 by volume) to prepare anelectrolytic solution having a LiPF₆ concentration of 1.0 mol/liter.

[0077] The test cell was prepared in the same manner as that of Example2-1,and a constant current charging and discharging test was conductedin the same manner as that of Example 2-1. The capacity of the 500^(th)cycle was 64% of the initial capacity.

Comparative Example 2-2

[0078] At first, LiBF₄ was dissolved in a mixture of ethylene carbonate(EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 by volume) to prepare anelectrolytic solution having a LiBF₄ concentration of 1.0 mol/liter.

[0079] The test cell was prepared in the same manner as that of Example2-1,and a constant current charging and discharging test was conductedin the same manner as that of Example 2-1. The capacity of the 500^(th)cycle was 46% of the initial capacity.

EXAMPLE 3-1

[0080] A lithium borate derivative, represented by the same formula asthat of Example 1-1,and ((CF₃)₂CHOSO₂)₂NLi were dissolved in a mixtureof ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 byvolume) to prepare an electrolytic solution having a lithium boratederivative concentration of 0.01 mol/liter and a ((CF₃)₂CHOSO₂)₂NLiconcentration of 0.99 mol/liter.

[0081] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0082] The test cell was prepared by the same manner as that of Example2-1. A constant current charging and discharging test was conducted bythe same manner as that of Example 2-1,except that the test wasconducted at an environmental temperature of 25° C. The capacity of the500^(th) cycle was 83% of the initial capacity.

EXAMPLE 3-2

[0083] A lithium borate derivative, represented by the same formula asthat of Example 1-1,and (CF₃CH₂OSO₂)₂NLi were dissolved in a mixture ofethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC=1:1 byvolume) to prepare an electrolytic solution having a lithium boratederivative concentration of 0.80 mol/liter and a (CF₃CH₂OSO₂)₂NLiconcentration of 0.10 mol/liter.

[0084] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0085] The test cell was prepared by the same manner as that of Example2-1. A constant current charging and discharging test was conducted bythe same manner as that of Example 2-1,except that the test wasconducted at an environmental temperature of 60° C. The capacity of the500^(th) cycle was 78% of the initial capacity.

EXAMPLE 3-3

[0086] A lithium borate derivative, represented by the followingformula, and ((CF₃)₂CHOSO₂)₂ NLi were dissolved in a mixture of ethylenecarbonate (EC) and ethylmethyl carbonate (EMC) (EC:EMC=1:1 by volume) toprepare an electrolytic solution having a lithium borate derivativeconcentration of 0.70 mol/liter and a ((CF₃)₂CHOSO₂)₂NLi concentrationof 0.30 mol/liter.

[0087] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0088] The test cell was prepared by the same manner as that of Example2-1. A constant current charging and discharging test was conducted bythe same manner as that of Example 2-1,except that the test wasconducted at an environmental temperature of 60° C. The capacity of the500^(th) cycle was 81% of the initial capacity.

EXAMPLE 3-4

[0089] A solution was prepared by adding acetonitrile to 70 parts byweight of a polyethylene oxide (average molecular weight: 10,000). Then,5 parts by weight of a lithium borate derivative, represented by thesame formula as that of Example 1-1,and 25 parts by weight of((CF₃)₂CHOSO₂)₂NLi were added to the solution. The resulting mixture wascast on a glass, followed by drying to remove the acetonitrile. Withthis, a polymer solid electrolyte film was prepared.

[0090] A corrosion test of an aluminum collector was performed using alaminate including the solid electrolyte film interposed between analuminum electrode (working electrode) and a lithium electrode. Thislaminate was prepared by press welding. When the working electrode washeld at 5 V (Li/Li⁺), there was no flow of current whatsoever. Followingtesting, although the surface of the working electrode was observed bySEM, there were no changes observed in comparison with that beforetesting.

[0091] The test cell was prepared by using the polymer solid electrolytefilm in place of the electrolytic solution and the separator.Furthermore, LiCoO₂ and lithium metal foil were respectively used forthe positive and negative electrodes. A constant current charging anddischarging test was conducted in the same manner as that of Example 2-4except that charging and discharging were repeated 100 times. As aresult, the initial discharge capacity was 120 mAh/g (the positiveelectrode capacity). The capacity of the 100^(th) cycle was 88% of theinitial capacity.

Comparative Example 3-1

[0092] At first, ((CF₃)₂CHOSO₂)₂NLi was dissolved in a mixture ofethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 byvolume) to prepare an electrolytic solution having a ((CF₃)₂CHOSO₂)₂NLiconcentration of 1.0 mol/liter.

[0093] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), corrosion current was observed. Following testing, thesurface of the working electrode was observed by SEM. With this, manypits were observed on its surface. It is assumed that these pits werecaused by corrosion.

[0094] The test cell was prepared in the same manner as that of Example2-1,and a constant current charging and discharging test was conductedin the same manner as that of Example 2-1, except that the test wasconducted at an environmental temperature of 25° C. The capacity of the500^(th) cycle was 62% of the initial capacity.

Comparative Example 3-2

[0095] At first, (CF₃CH₂OSO₂)₂NLi was dissolved in a mixture of ethylenecarbonate (EC) and diethyl carbonate (DEC) (EC:DEC=1:1 by volume) toprepare an electrolytic solution having a (CF₃CH₂OSO₂)₂NLi concentrationof 1.0 mol/liter.

[0096] A corrosion test of an aluminum collector was performed in thesame manner as that of Example 1-1. When the working electrode was heldat 5 V (Li/Li⁺), corrosion current was observed. Following testing, thesurface of the working electrode was observed by SEM. With this, manypits were observed on its surface. It is assumed that these pits werecaused by corrosion.

[0097] The test cell was prepared in the same manner as that of Example2-1,and a constant current charging and discharging test was conductedin the same manner as that of Example 2-1, except that the test wasconducted at an environmental temperature of 60° C. The capacity of the500^(th) cycle was 58% of the initial capacity.

Comparative Example 3-3

[0098] At first, a lithium borate derivative, represented by the sameformula as that of Example 1-1,was dissolved in a mixture of ethylenecarbonate (EC) and ethylmethyl carbonate (EMC) (EC:EMC=1:1 by volume) toprepare an electrolytic solution having a lithium borate derivativeconcentration of 0.8 mol/liter.

[0099] The test cell was prepared in the same manner as that of Example2-1,and a constant current charging and discharging test was conductedin the same manner as that of Example 2-1, except that the test wasconducted at an environmental temperature of 60° C. The capacity of the500^(th) cycle was 64% of the initial capacity.

[0100] The entire disclosure of Japanese Patent Applications No.2000-360540 and 2000-360541 each filed on Nov. 28, 2000, and No.2001-257159 filed on Aug. 28, 2001,including specification, claims andsummary, is incorporated herein by reference in its entirety.

What is claimed is:
 1. An electrolyte for an electrochemical device,said electrolyte comprising: a first compound that is an ionic metalcomplex represented by the general formula (1); and at least onecompound selected from the group consisting of second to fourthcompounds respectively represented by the general formulas (2) to (4),fifth to ninth compounds respectively represented by the generalformulas A^(a+)(PF₆ ⁻)_(a), A^(a+)(ClO₄ ⁻)_(a), A^(a+)(BF₄ ⁻)_(a),A^(a+)(AsF6⁻)_(a), and A^(a+)(SbF₆ ⁻)_(a), and tenth to twelfthcompounds respectively represented by the general formulas (5) to (7).

 wherein M is a transition metal selected from the group. consisting ofelements of groups 3-11 of the periodic table, or an element selectedfrom the group consisting of elements of groups 12-15 of the periodictable; A^(a+) represents a metal ion, hydrogen ion or onium ion; arepresents a number from 1 to 3; b represents a number from 1 to 3; p isb/a; m represents a number from 1 to 4; q is 0 or 1; R¹ represents aC₁-C₁₀ alkylene group, C₁-C₁₀ halogenated alkylene group, C₄-C₂₀ arylenegroup or C₄-C₂₀ halogenated arylene group, these alkylene and arylenegroups of said R¹ optionally having substituents and hetero atoms, oneof said R¹; being optionally bonded with another of said R¹; each of X¹and X² independently represents O, S or NR²; R² represents a hydrogen,C₁-C₁₀ alkyl group, C₁-C₁₀ halogenated alkyl group, C₄-C₂₀ aryl group orC₄-C₂₀ halogenated aryl group, these alkyl and aryl groups of said R²optionally having substituents and hetero atoms, at least two of said R²being optionally bonded together to form a ring; each of x, y and zindependently represents a number from 1 to 8 each of Y¹, Y² and Y³independently represents a SO₂ group or CO group; and each of R³, R⁴ andR⁵ independently represents an electron-attractive organic substituentoptionally having a substituent or a hetero atom, at least two of saidR³,R⁴ and R⁵ being optionally bonded together to form a ring, at leastone of said R³, R⁴ and R⁵ being optionally bonded with an adjacentmolecule to form a polymer.
 2. An electrolyte according to claim 1,wherein said at least compound is selected from the group consisting ofsaid second to ninth compounds.
 3. An electrolyte according to claim 1,wherein said at least one compound is selected from the group consistingof said tenth to twelfth compounds.
 4. An electrolyte according to claim1, wherein said M is an element selected from the group consisting ofAl, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf,and Sb.
 5. An electrolyte according to claim 4, wherein said M is anelement selected from the group consisting of Al, B and P.
 6. Anelectrolyte according to claim 1, wherein said A^(a+) is a lithium ionor quaternary ammonium ion.
 7. An electrolyte according to claim 1,wherein said q of the general formula (1) is
 0. 8. An electrolyteaccording to claim 1, wherein a molar ratio of said first compound tosaid at least one compound is 5:95 to 95:5.
 9. An ion conductor for anelectrochemical device, said ion conductor comprising: an electrolyteaccording to claim 1; and a member selected from the group consisting ofa nonaqueous solvent, a polymer and a mixture thereof, said memberdissolving therein said electrolyte.
 10. An ion conductor according toclaim 9, wherein said nonaqueous solvent is an aprotic solvent, andthereby said ion conductor is an electrolytic solution.
 11. An ionconductor according to claim 10, wherein said nonaqueous solvent is amixture of a first aprotic solvent having a dielectric constant of 20 orgreater and a second aprotic solvent having a dielectric constant of 10or less.
 12. An ion conductor according to claim 9, wherein said A^(a+)is a lithium ion.
 13. An ion conductor according to claim 9, whereinsaid polymer is an aprotic polymer, and thereby said ion conductor is asolid electrolyte.
 14. An ion conductor according to claim 9, which hasa concentration of said electrolyte within a range of from 0.1 mol/dm³to a saturated concentration.
 15. An ion conductor according to claim14, wherein said concentration is within a range of from 0.5 mol/dm³ to1.5 mol/dm³.
 16. An electrochemical device comprising: (a) first andsecond electrodes; and (b) an ion conductor receiving therein said firstand second electrodes, said ion conductor comprising: (1) an electrolyteaccording to claim 1; and (2) a member selected from the groupconsisting of a nonaqueous solvent, a polymer and a mixture thereof,said member dissolving therein said electrolyte.
 17. An electrochemicaldevice according to claim 16, which is a cell or an electricaldouble-layer capacitor.
 18. An electrochemical device according to claim17, wherein said cell is a lithium cell or a lithium ion cell.